Light Scattering in Random Media (Experiment)

Brief History of the ILP Bio-Optical Imaging Lab

During the late 1990s, ILP extended its research programs to include the systematic studies of the scattering properties of electromagnetic radiation fields through various heterogeneous dielectric media. This research area seemed to be a promising realm in which ILP's general research philosophy could be successfully applied.

On an purely exploratory basis, ILP performed a very limited and rough series of experimental investigations in August 2003 of how laser light intensity would fall off inside an aquarium filled up with milk. This period was characterized by failures and disappointments. A simple measurement took our senior Michael Bell more than two hours, because each detected light intensity had to be read off from a multi-meter, recorded by hand, and the source-detector spacing had to be manually increased. Nothing was automized, and we realized that the old He-Ne lasers we used had unacceptable intensity fluctuations on short- and long-time scales.

In January 2004, ILP gave the green light for establishing a state-of-the-art Bio-Optical imaging lab. The first element needed was an oversized but highly accurate x-y translation stage to permit us to scan the laser intensity across an area of 0.7 m x 1.2 m with an error of less than 0.5 mm. Senior Peter Peverly (now studying for a Ph.D. in Optics at U of Rochester) developed the necessary virtual interfaces using LabView to control the stepper motors and record the voltage from the light detectors. With the valuable advice from Prof. Clark, a laser experimentalist, we discussed a sketch of the apparatus with model maker Jim Dunham. After the usual delay in ordering materials, the stage was completed on July 20, 2004.

In May 2004, we hired Sawyer Campbell, who just graduated from high school, to become ILP's lab manager for the next four years. During summer 2004, the team of Campbell, Peverly and Bell (now a Physics Ph.D. student at UIUC) systematically optimized the LabView software modules, tested the detector efficiency and the fluctuations of the newly purchased temperature controlled diode laser system, measured angular emission profiles of various multi-mode optical fibers using a rotating stage, replaced cables, built screened aluminum casings and converted room 305 in Moulton Hall (formerly a photo lab) into an efficient work space with internet access, shelves, desks, chairs and improved lighting.

For the next few years, we have planned a truly exciting series of experiments that will be guided by our theoretical work. Based on our postdoc Dr. Menon's theory and inversion algorithm, we will attempt to provide a first measurement of the scattering coefficient for the host medium, as well as its anistropy factor g, going beyond the usual measurement of only the reduced scattering coefficient. We plan to measure for the first time the transition from the Maxwell regime, to the Boltzmann regime, to the diffusive light regime. Another series of experiments will verify the dark-cone effect that we predicted in 2002 based on Monte Carlo simulations. We will also begin to explore the feasibility of laser-based imaging schemes that were developed in the last few years to detect an embedded object inside a medium and for which a patent application to ISU is pending.

Selected Publications

"Laser beam widening mechanisms in turbid media"
S.D. Campbell, T.P. Garvin, I.L. Goodin, Q. Su and R. Grobe, Las. Phys. 19, 238 (2009).

"Limitations of decomposition based imaging of longitudinal absorber configurations"
S.D. Campbell, S.D. Grobe, I.L. Goodin, Q. Su and R. Grobe, Phys. Rev. A 77, 023821 (2008).

"Decomposition based imaging with fiber and ccd camera detections"
S.D. Campbell, I.L. Goodin, S.D. Grobe, Q. Su and R. Grobe, J. Opt. Health Sci. 1, 115 (2008).

"Impact of large-angle scattering on diffusively backscattered light"
S. Campbell, A. O'Connell, G.H. Rutherford and R. Grobe, Opt. Lett. 32, 560 (2007).

"Scaling of light scattering with density of scatterers"
S. Campbell, S. Menon, Q. Su, G.H. Rutherford and R. Grobe, Las. Phys. 17, 117 (2007).

"Decomposition based recovery of absorbers in turbid media"
S.D. Campbell, I.L. Goodin, S.D. Grobe, Q.Su and R. Grobe, Phys. Rev. A 76, 063802 (2007).

"Velocity half-sphere model for multiple scattering in a semi-infinite medium"
S. Menon, Q. Su and R. Grobe, Phys. Rev. E 75, 053817 (2007).

"Light scattering regimes along the optical axis in trubid media"
S. Campbell, A. O'Connell, S. Menon, Q. Su and R. Grobe, Phys. Rev. E 74, 061909 (2006).